The Session Initiation Protocol (SIP) is a control protocol for application layers, i.e. a signaling protocol for establishing, modifying and clearing down multimedia sessions. SIP is known from “SIP: Session Initiation Protocol”, RFC 3261, June 2002, http://www.ietf.org. These multimedia sessions are taken to mean multimedia conferences, Internet telephone calls (Voice Over IP) and similar applications for example. SIP can be used to invite participants into multimedia sessions and also to add them to multimedia sessions which are already active. One of the capabilities of SIP is to locate a participant and thereby a specific terminal, assign an address to the terminal and also to redirect connections.
SIP has been selected by 3GPP (3GPP—Third Generation Partnership Project) as the signaling protocol for the IP multimedia subsystem (IMS—IP Multimedia Subsystem, IP—Internet Protocol). Thus IMS has been used to help provide an expansion of the UMTS (UMTS—Universal Mobile Telecommunications System) core network for implementing IP-based services.
The publications IETF RFC 3313, “Private Session Initiation (SIP), Extension for Media Authorization”, January 2003, 3GPP TS 24.229 “IP Multimedia Call Control Protocol based on SIP and SDP, Stage 3” and 3GPP TS 23.203 “End-to-End Quality of Service Concept and Architecture” describe a method with which data connections which are needed for an SIP-based session can be authorized. The quantity of data which is to be exchanged via this data connection is detected in the GPRS (GPRS—General Packet Radio System) network. However this system does not allow any recording or filtering of the transmitted data messages at application level.
The German patent application with the file reference 10 2004 009 289.3 “Verfahren zur Steuerung und Auswertung eines Nachrichtenverkehrs einer Kommunikationseinheit durch eine erste Netzwerkeinheit innerhalb eines Mobilfunksystems sowie dazugehörige Kommunikationseinheit und erste Netzwerkeinheit” (Method for control and evaluation of message traffic of a communication unit within a mobile radio system as well as associated communication unit and first network unit) describes a method with which one or more messages of the message traffic of a communication unit are forwarded on the basis of one or more items of utilization information, blocked and/or logged in a log file.